Well, I know it was less than 100k total users when it was just the new ARMA 2 mod on the scene that only the active playerbase for that knew about (April/May). After it had gone viral and exploded in popularity, they still only had 400k users, even though they already reached more than 100k daily players (June/early-July). That total users figure had DOUBLED after the Steam Summer Sale, and then surpassed a million in the first week of August. The daily player count peaked at around 120k or so, but has been declining ever so slightly since then, despite the total users growing to 1.24 million as of today.

There is no way in hell that massive spike of new players in the latter half of July was due to people who already owned the game suddenly taking an interest in playing. Maybe some had ARMA 2 and just needed to buy the expansion, like I did, but the majority were buying Combined Ops. You could argue that a good chunk of that "total players" number is actually people buying extra CD keys, whether to have a second+ character or to replace one that was banned, but those sales all look the same to the developer.